Photoelectrostatic relay



Jan. 14, 1936.

H. NELSON I 2,027,751

PHOTO ELECTROSTATIC RELAY Filed Feb. 15, 1954 I 24 INVENTOR HERBERTNELSON -n% |||vq\\\ BY WW ATTORNEY voltage actuated device, the

rim Jan; 14, 1936 UNITED STATES PATENT OFFICE PHOTOEI-ICIIOSTAHG mayBerber-thicken,

Radioman! Delaware Orange, N. 1., signalmambpplieationl'ebnarylilmsahllim'lllfll SClainu. ((123-275) not beencommercially practical on account o1 highcostandlackotrus.

One object of my invention is to provide acommercianypracticalrelaywhichwillcontrolaworkcircuitandwillrespondtosuchnnall currents, for example. less than amicroampere, thatitmaybeoperatedbyadevicesuchasa photo-tube.

Anotherobjectistoprovidearelaywhichmayconvenientlybemountedinavacuumtube' containing an electronic devicefor operating therelayandthusobtainacompactruggeddevice with theadvantages 0! a vacuum make and break relay.

A further object is to provide a simple and compact photo relay whichwill open and cme a controlled circuit in response to variations inlight intensities, and which is a unitarydevicethatmaybeutilizedtoreplacetheusual combination of photo-tube,amplifier, and electic relay.

Inaccordancewithmyinventionapairot rdatively movable contacts connectedin the circuittobecontrolledaremoimtedinasealedorevacuatcdbulbsoastobemovableintoand outottintovariationsin theelectrostatic field of an electrostatic actuator, such as a metal plate,which may be charged to such a potential that its electrostatic field isgreat enough to actuate the circuit controlling contacts. As the relayis essentially a necessary operating voltage may be obtained from acurrent which is negligible as compared with the current required forthe usual cm'rent operated ebch-omagnetic relay. The relay may beconnected externally to a photo-tube or similar device, but for mostcommercial purposes I prefer to comblue the relay and the photo-tubeinto a simple compact and unitary device in which the circuitcontrolling contacts and the electrostaticactuatorplatearemountedinthebulbotthe photo-tube with the actuator platein connected to the photo-ca hode so that a h ghcrimpedanceintheoutnitdrcuit the photo-tube will produce onplateottherelayavoltageorcharge dependent on the amount of photo currmtthereforetheelectrostaticfleldotthecharged iallingonthephoto-cathode,andis tly ruggedfm-commercialuse.

The novel features which are characteristicotmyinveniaonaresetiorthwithgreaterparticularity in the a claims, butthein- Suitableforusewiththerelay showninFigurezwithexternalto aphoto-tube.

'lhecircuitopmingandclosingrelay,whlchformspartofthepreferredformofdevice showninlieureLhaaasshowninl'igures1and2,anevacuatedbulb5,withaiourprong basetatoneendandacontactcaplattheotherend,enclosingtheelectrodeswhichare moimtedoniheusualpressl. Therelatively movable contacts for making and breaking the controlledcircuit comprise two fixed contactsiandllsuchastwoparallelnickelwireaand a cooperating movable contact ll,whkzh may conveniently be a thin resilient strip or bladeofnickelmountedatitslowerendonthepress to project between the two flxedcontacts. 'Ihisnickelstripllismountedwithitssidesparalleltotheflxedcontacmandistensionedtonormallyengageoneoftheflxedcontacts, suchasthecontact.

Themmblecontactorstripdnlckelllismovedrelativelytoflieflxedcontactsbyancleetrostatic actuator, such as ametal plate l2 mounted parallel to the strip ll and close enough to itso that the upper end of the strip acts as a plate armature parallelwith and close to the actuator plate and of such area that the stripwill be moved from the contact 9 into engagement with the contact I0 inresponse to the electrostatic attraction exerted on the armature by theactuator plate when the plate is charged. The actuator plate [2 iselectrically connected to the contact cap 7, and is preferably held inproper relation to the contacts by some kind of an insulating spacer,such as a glass head or rod 13, which may conveniently carry a gettercapsule 14 for holding a mixture for developing caesium vapor forsensitizing the photocathode. I have obtained good results with such arelay in which the flat strip II is of resilient nickel, about twothousandths of an inch thick. about one-eighth of an inch wide, andabout six inches long, and a flat sheet nickel actuator plate l2, aboutone-half inch square. The area of such an actuator plate will ordinarilybe willcient so that the relay operates satisfactorily. A suitablespacing between the actuator plate and the metal strip is about ten onethousandths of an inch. In this relay a potential of from 400 to 500volts on the actuator plate exerts suflicient pull by electrostaticattraction to move the strip H over against the contact I, which acts asa stop toprevent the armature coming into contact with and dischargingthe actuator plate.

The electrostatic charge for actuating the make and break contacts maybe impressed on the actuator plate l2 from an external source throughthe contact cap I in the simple relay shown in Figure 2, or may bederived from a photo-tube comprising a photo-cathode and a cooperatinganode enclosed in the bulb 5 to form part of the photo relay shown inFigure 1. The photo-tube maybe of various forms, but I have shown aconventional type of two electrode photo-tube comprising asemi-cylindrical photocathode 15 supported from the press on a lowleakage insulator comprising a glass bead l8, which is to advantageprotected by an insulating skirt II. The photo-cathode I5, preferably ofthe caesiated type, may have on its concave side a surface of oxidizedsilver coated with caesium developed from a caesium compound in thegetter capsule l4, in' accordance with the usual practice in makingphotosensitive surfaces of this type. One of the photo-tube electrodes,preferably the photo-cathode I 5, is connected to the actuator plate I2and to the top cap 1, preferably by a connector I8 inside the bulb. Thephoto-tube anode may be a straight rod anode l9 mounted on the press atabout the center of curvature of the semi-cylindrical photocathode.

Figure 3 shows diagrammatically an application of the photo relay shownin Figure 1 as a device for counting or indicating interruptions of abeam of light. A source 20 of potential, preferably alternating, has oneterminal connected to the photo-tube anode l9 and the other terminal tothe photo-cathode l5 and actuator plate l2 through a high impedance,such as a grid leak 2| of about 5000 megohms resistance, shunted by amica condenser 22 of about 100 micromicrofarads capacity and of as highleakage resistance as feasible. The fixed contacts 9 and it areconnected to controlled circuits 23 and 24, respectively. A light source25, such. I

as an incandescent lamp, produces a light beam which falls on theconcave surface of the photocathode l5.

voltage drop across the impedance in the output current of -thephoto-tube is large enough to charge the actuator plate to a voltage atwhich its electrostatic field causes the nickel strip l I to be pulledaway from contact 9, opening the circuit 23 and closing circuit 24. Whenthe light beam is interrupted, the photo current from the photo-cathodedrops, the voltage across the impedance drops correspondingly, and theelectrostatic charge on the actuator plate also drops, whereupon thenickel strip II is released and swings back into contact with the fixedcontact 9, closing circuit 23 and opening circuit 24. I have found thatwith this circuit the strip II is attracted and circuit 23 opened whenthe photo-tube current exceeds about one-tenth of a microampere and isreleased and returns to its cathode 21 and an anode 28. A battery 29 of5 a voltage which will charge the actuator plate l2 to a potentialsufiicient to operate the relay has its negative terminal connected tothe photo-cathode 21 of the photo-tube and also through the top cap 1 tothe actuator plate l2 of the relay; The positive terminal of the battery29 is connected through a grid leak resistor 30 to the anode 28 of thephoto-tube and to the movable contact for the nickel strip H. cuit 23 isclosed as long as the'potential across the photo-tube 26 is less thanthe critical potential at which the electrostatic attraction exerted bythe actuator plate I2 on the strip II is suflicient to overcome thetension of the strip and move it away from the contact 9.

When the critical potential is exceeded, the strip H is pulled towardthe actuator plate and into contact with the fixed contact l9, closingcircuit 24. I have found that in this arrangement with a battery 29 ofabout 500 volts and of a resistor 39 of about 5000 megohms resistance,the critical potential across the photo-tube 26 at which the strip H ispulled over to the actuator plate is about 430 volts, and that when thiscritical potential drops to about 350 volts the strip II is released andresumes its original position. In this arrangement the actuator plate I2is charged high enough to attract the strip l I and break the circuit 23when the phototube current decreases below about fourteenhundredths of amicroampere, and its potential decrease to a point at which it releasesthe strip II when the photo-tube current increases to abouttwenty-eight-hundredths of a microampere.

Tests have shown that my electrostatic relay will handle satisfactorilyat the circuit controlling contacts 9 and H currents as high as 3amperes at 6 volts, and that the relay is suf'flciently rugged to besatisfactory for ordinary use, although in some cases it may bedesirable to shield the relay from mechanical vibration.

While I have indicated the preferred embodiment of my invention of whichI am now aware and have also indicated only one specific appli- Cir-When the light beam is uninter-' rupted and the photoelectric current islarge, the

cation for which my invention may be employed, it will be apparent thatmy invention is by no means limited to the exact forms illustrated orthe use indicated, but that many variations may be made in theparticular structure used and the purpose for which it is employedWithout departing from the scope of my invention as set forth in theappended claims.

What is claimed as new is:

l. A unitary photo relay comprising a highly evacuated bulb having apress at one end and enclosing a fixed contact mounted on said press, aresilient blade mounted at one end on said press and tensioned tonormally engage said fixed contact, a support wire projecting from saidpress into said bulb alongside said blade, a low leakage insulator onthe inner end of said support, a sheet metal photocathode supported onsaid insulator beside said blade and sensitized to light on its surfaceopposite said blade, a rod anode mounted on said press parallel to andon the sensitized side of said photocathode, an insulating spacermounted on said press adjacent the upper end of said photo-cathode, anactuator plate mounted on said spacer near the free end of said bladeparallel to the side of said blade, and an electrical connection betweensaid photocathode and said actuator plate and extending through theother end of said bulb.

Z. A unitary photo relay comprising a highly evacuated bulb having apress at one end and enclosing an insulating spacer on and parallel tosaid press, a fixed contact mounted on said insulating spacer, acooperating movable contact mounted on said press to engage said fixedcontact and comprising a plate armature, an actuator plate mounted onsaid insulating spacer adjacent and parallel to said plate armature, alow leakage insulator mounted on said press, a curved sheet metalphotocathode mounted on said insulator beside said movable contact withthe concave surface facing away from said contact and sensitized tolight, a cooperating anode mounted on said press on the concave side ofsaid photo-cathode, an internal electrical connection between saidactuator plate and said photo-cathode and extending through the otherend of said bulb, leads in said press connected to said contacts and tosaid anode, and a support for s .d insulator embedded in and projectingfrom said press.

3. A unitary photo relay comprising a highly evacuated bulb having apress at one end and enclosing a fixed contact, and a cooperatingmovable contact mounted on said press, said movable contact comprising aplate armature, a photo-tube assembly comprising a curved sheet metalphoto-cathode sensitized to light on its concave side and mounted besidesaid movable contact with its convex side toward said contact and ananode mounted on the concave side of said photo-cathode, a glass beadspacer mounted on said press adjacent said contacts and saidphotocathode and rigidly connected to said fixed contact and to saidphoto-cathode, an actuator plate mounted on said glass bead spaceradjacent and parallel to said plate armature, a photocathode supportcomprising a low leakage insulator mounted on a support in said pressand carrying said photocathode, and an electrical connection betweensaid actuator and said photocathode and extending through the other endof said bulb.

4. A unitary photo relay comprising a highly evacuated bulb having apress at one end and enclosing a fixed contact, an actuator plate, aninsulating spacer for spacing said fixed contact and said actuatorplate, a resilient blade mounted at one end on said press with the otherend adjacent said fixed contact and with its side parallel to saidactuator plate, a sheet metal photocathode mounted beside said bladewith its surface opposite said blade sensitized to light, and acooperating anode mounted adjacent said sensitized surface, a support onsaid insulating spacer for said photo-cathode, an electrical connectionelectrically connecting said actuator plate and said photocathode to atermi- 35 nal at the other end of said bulb, and a photocathode supportcomprising a low leakage insulator mounted on a support in said press.

5. A photoelectric relay comprising a highly evacuated envelopeenclosing an electrostatic relay including an actuator plate and acooperating movable electrode, a photo-cathode comprising a metal sheetmounted beside said movable electrode and sensitized to light on thesurface facing away from said electrode, an anode adjacent saidsensitized surface, an insulating support for said actuator plate, arigid metallic conductor connecting said actuator plate and saidphoto-cathode, and a conductor extending through the wall of saidenvelope and electrically connected to said actuator plate and saidphotocathode.

HERBERT NELSON.

